1. Field of the Invention
This invention relates to relates generally to minimally invasive treatment of organs inside the body. More particularly, this invention relates to determination of ablation sites for ablation treatments applied to cardiac tissue.
2. Description of the Related Art
The meanings of certain acronyms and abbreviations used herein are given in Table 1.
TABLE 1Acronyms and AbbreviationsAFAtrial FibrillationCFAEComplex Fractionated Atrial ElectrogramDFDominant FrequencyGPGanglionated PlexiLALeft AtriumMIBG123I-metaiodobenzylguanidineMRIMagnetic Resonance ImagingSPECTSingle Photon Emission Computed Tomography
Cardiac arrhythmias, such as atrial fibrillation, occur when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm.
Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. By selectively ablating cardiac tissue by application of energy via a catheter, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions.
Successful catheter-based ablation for atrial fibrillation (AF) often entails accurate execution of a relatively complex therapeutic plan comprising many ablation points. The procedure is challenging and time consuming. For example, in the document A New Approach for Catheter Ablation of Atrial Fibrillation: Mapping of the Electrophysiologic Substrate, Nademanee et al., J. Am. Coll. Cardiol., 2004; 43(11): 2044-2053, it was proposed that atrial fibrillation may be treated by ablating sites exhibiting a complex fractionated atrial electrogram (CFAE). The authors identified areas of CFAE during atrial fibrillation, and then applied radiofrequency ablation to these areas. As a result of the ablation, the atrial fibrillation was resolved in the large majority of the cases.
Nademanee's method requires a human operator to read electrograms to identify sites of CFAE. Commonly assigned U.S. Patent Application Publication No. 2007/0197929, which is herein incorporated by reference, facilitates the procedure by disclosing automated detection and mapping of areas of complex fractionated electrograms within cardiac chambers. Commonly assigned U.S. Patent Application Publication No. 20090192393, which is herein incorporated by reference, discloses automatic detection and mapping of ganglionated plexi that are found within areas of complex fractionated electrograms in cardiac chambers. Functional maps indicating a spatial distribution of the ganglionated plexi and the relative numbers of complex fractionated electrograms are produced for display.
More recently, SPECT and planar cardiac sympathetic imaging using 123I-metaiodobenzylguanidine (MIBG) has become sufficiently well known to indicate standardization, as described by Albert Flotats et al., Proposal for standardization of 123I-metaiodobenzylguanidine (MIBG) cardiac sympathetic imaging by the EANM Cardiovascular Committee and the European Council of Nuclear Cardiology, Eur J Nucl Med Mol Imaging (2010) 37:1802-1812. Techniques disclosed in Rozovsky et al., Added Value of SPECT/CT for Correlation of MIBG Scintigraphy and Diagnostic CT in Neuroblastoma and Pheochromocytoma, AJR 2008; 190:1085-1090 may be adapted for imaging ganglionated plexi in the heart.
Evaluation of epicardial fat may also be useful in identifying ablation points. For example, commonly assigned U.S. Patent Application Publication No. 2008/0058657, which is herein incorporated by reference, describes obtaining an endocardial map by constructing a matrix relationship between a small number of endocardial points and a large number of external receiving points using a multi-electrode chest panel. Magnetic resonance imaging (MRI) and computed tomography have also been applied to the evaluation of epicardial fat, as described for example in Abbara et al., Mapping Epicardial Fat With Multi-Detector Computed Tomography To Facilitate Percutaneous Transepicardial Arrhythmia Ablation, European Journal of Radiology 57 (2006) 417-422, and in Kriegshauser et al., MR Imaging of Fat in and Around the Heart, AJR 155:271-274, August 1990.
It has been noted in Dewire, J. & Calkins, State-of-the-art and Emerging Technologies for Atrial Fibrillation Ablation, H. Nat. Rev. Cardiol. 7, 129-138 (2010) that there is an interest in the development of new tools and strategies that will improve the safety and efficacy of AF ablation, shorten procedure time, and allow ablation to be performed by operators with little prior experience of the technique.